In the current production of a semiconductor element, a physical vapor deposition method (PVD method) by sputtering is mainly used in a method for forming a thin film of a wiring barrier, a capacitor dielectric and an electrode. However, in a semiconductor production in the next generation or later, it is required to form a uniform and thin film on a surface having a complicated three-dimensional structure of a miniaturized element. Therefore, the PVD method which is difficult to form a uniform film on a surface having concave and convex is not suitable. For this reason, a thin film formation method by CVD method which decomposes a raw material gas to deposit a film, or an atomic layer deposition method (ALD method) which decomposes a raw material adsorbed on a substrate surface to deposit a film is recently investigated.
Raw materials having appropriate vapor pressure and thermal stability and capable of vaporizing in a stabilized supply amount are selected in production raw materials for forming a thin film by CVD method or ALD method. Furthermore, it is one of necessary conditions that a film can be formed with a uniform film thickness on a surface having a complicated three-dimensional structure. Additionally, to stably vaporize in a constant supply amount, a liquid is preferred.
Titanium, titanium nitride and silicon-containing titanium nitride are nominated as materials of a barrier film of a semiconductor element and an electrode film of a capacitor in the next generation or later. Furthermore, titanium oxide and titanium-containing oxide are nominated as materials of a capacitor dielectric film.
Tetrakisamide complex Ti(NRR′)4 (R and R′ are a methyl group or an ethyl group) and the like have hitherto been investigated as a raw material that forms a thin film of titanium, titanium nitride and silicon-containing titanium nitride by CVD method and ALD method (for example, see Patent Document 1). However, it is known that Ti(NRR′)4 has extremely high reactivity to water and reacts with a slight amount of water contained in a carrier gas, a reaction gas or the like used in film formation, and that oxygen is liable to be incorporated in a film formed. For example, it is reported that 10 atm % or more of oxygen is contained in a titanium nitride film formed by a remote plasma ALD method using titanium tetrakis(dimethylamide) Ti(NMe2)4 as a raw material (for example, see Non-Patent Document 1). A film containing oxygen has high specific resistance value, and therefore, does not satisfy the demand characteristics of a barrier layer. In other words, those tetrakisamide complexes are not preferred as a raw material for barrier layer formation.
On the other hand, tetraisopropoxotitanium Ti(OiPr)4, (diisopropoxo)(bis(2,2,6,6-tetramethylheptanedionato))-titanium Ti(OiPr)2(THD)2, tetrakis(2-methoxy-1-methyl-1-propoxo)titanium Ti(MMP)4 and the like have been investigated as raw materials for forming a titanium oxide film and a titanium-containing oxide film by CVD method of ALD method.
Where it is attempted to form a film using Ti(OiPr)4 as a raw material, Ti(OiPr)4 is extremely unstable to water, and as a result, there is the possibility that contamination of a slight amount of water vapor into a piping in an apparatus forms fine powder of titanium oxide, thereby clogging a pipe. Furthermore, where Ti(OiPr)4 is blown to a substrate and decomposed thereon, an alcohol is generated, and the alcohol is decomposed into water and an alkene. The water reacts with undecomposed Ti(OiPr)4 to form a fine powder of titanium oxide, and the fine powder is adhered to a film formation chamber and an exhaust port, resulting in the decrease of productivity. For this reason, Ti(OiPr)4 is not preferred as a raw material for the formation of a thin film used in a semiconductor element (see Patent Document 2).
Where a film is formed using Ti(OiPr)2(THD)2 or Ti(MMP)4, particularly where a titanium-containing composite oxide film is formed by CVD method, volatilization properties and decomposition properties of those to other metal supply source raw materials greatly differ, and as a result, there was the problem that it is difficult to control a composition of a thin film in a preferred ratio, thereby decreasing productivity.
Non-Patent Document 1: Journal of The Electrochemical Society, Vol. 152, page G29 (2005)
Patent Document 1: JP-A-2006-93551
Patent Document 2: JP-A-2004-196618